In the scientific literature, the term Maya blue refers to a “turquoise” brilliant shade of blue that is found on murals and archaeological artifacts, for example, throughout Mesoamerica. It is described in the literature as being composed of palygorskite clay and indigo, that when mixed and heated, produce the stable brilliant blue color similar to that found in Mesoamerica. Proposed methods of preparation were performed with the intent of trying to replicate the blue color found at the historical sites and to reproduce the techniques employed by the original Maya.
H. Van Olphen, Rutherford Gettens, Edwin Littman, Anna Shepard, and Luis Torres were involved in the examination of organic/inorganic complex paint from the 1960's to the 1980's. In early studies, Littman and Van Olphen published information specifically on the synthesis of the Mayan organic/inorganic complex (Littman, Amer. Antiquity, 45:87-101, 1980; Littman, Amer. Antiquity, 47:404-408, 1982; Olphen, Amer. Antiquity, 645-646, 1966; Olphen, Science, 154:645-646, 1966). Their work did not describe the technique for making the colorant, nor explain the stability of the organic/inorganic complex. However, the results of their two decades of studies with respect to the ancient paint laid a foundation of knowledge for future investigators.
Littman synthesized indigo-attapulgite complexes and verified that his synthetic version was indistinguishable from the original pigments found in the pre-Hispanic murals and artifacts (Littman, Amer. Antiquity, 45:87-101, 1980; Littman, Amer. Antiquity, 47:404-408, 1982). The prepared samples had the same physical and chemical characteristics as the authentic Maya blue examined. Littman concluded that the remarkable stability of the attapulgite was due to the heat treatment the attapulgite received during the synthesis. Others have also synthesized compounds similar to that of Maya blue by a number of routes (Tones, Maya Blue: How the Mayas Could Have Made the Pigment, Mat. Res. Soc. Symp., 1988). They employed the Gettens test to determine whether the laboratory synthesis of Maya blue was indeed authentic with the same chemical resistant properties (Gettens, Amer. Antiquity, 27:557-564, 1962). The test was necessary because initial attempts of simply mixing the palygorskite clay produced the color of Maya blue but the mixture did not possess the same chemical properties as the original organic/inorganic complex samples.
Previous literature discussions of pH pertain to the alkaline pH required to reduce the indigo prior to contacting it with the clay (Littman, Amer. Antiquity, 45:87-101, 1980; Littman, Amer. Antiquity, 47:404-408, 1982). Moreover, there was a lack of understanding regarding the chemistry for producing stable and nontoxic paint systems by combining dyes and pigments with fibrous clays. U.S. Pat. No. 3,950,180 describes color compositions that involve cationic organic basic colored compounds complexed to alkali-treated inorganic substances.
More recently, several patents and patent applications discussed indigo and related organic dyes complexed in an ionic interaction with inorganic supports. PCT Publication No. WO 01/04216 also describes ionic interactions in color compositions, wherein organic dyes undergo ion exchange with charged inorganic clays.
U.S. Pat. No. 3,950,180 covers a method of manufacturing color compositions that include zeolite and montmorillonite. U.S. Pat. No. 5,061,290 covers a method of using indigo derivatives as a dyeing agent. U.S. Pat. No. 4,246,036 covers the method of manufacturing color compositions that are comprised of asbestos-cement. U.S. Pat. No. 4,640,862 covers color compositions that are used for coating an expanded polystyrene “drop-out” ceiling tile. U.S. Pat. No. 4,868,018 covers color compositions that are used with a mixture of epoxy resin, epoxy resin hardener, and portland cement to form a coating which can be applied to a surface to form simulated marble products. U.S. Pat. No. 4,874,433 covers a method for encapsulating color compositions in and/or to a zeolite. U.S. Pat. No. 5,574,081 covers a method of manufacturing waterborne clay-containing emulsion paints with improved application performance using color compositions. U.S. Pat. No. 5,972,049 covers the method of manufacturing and using color compositions to form dye carriers used in the dyeing process for hydrophobic textiles. U.S. Pat. No. 5,993,920 covers the method of manufacturing and using color compositions with stone powder and/or cement powder, fine sawdust and/or the heart of a kaoliang stalk and other materials to form an incombustible artificial marble. U.S. Pat. No. 6,339,084 covers the method of manufacturing thiazine-indigo pigments. U.S. Pat. No. 6,402,826 covers the method and manufacturing of color compositions for paper coating.
U.S. Pat. Nos. 7,052,541 and 7,429,294 describe color compositions comprising neutral indigo derivative pigments and dyes complexed to the surface of inorganic clays. These materials are useful as paints and coatings for artistic and industrial purposes, including use in cements, plastics, papers and polymers. Upon grinding and heating the organic and inorganic component as solid mixtures or in aqueous solutions, the resulting color compositions have unprecedented stability relative to the original starting materials. U.S. Pat. No. 7,425,235 describes the use of similar starting materials in methods that rely on UV-light for preparing color compositions.
Organic-inorganic titanate hybrid pigments have been developed that are non-bleeding, have good light-fastness, exhibit maximum gloss, opacity, and strength. These pigments are organic-inorganic titanate hybrids comprising organic colorants attached to the surface of a titanate carrier, as disclosed by U.S. Patent Publication No. 2008/0216711, incorporated by reference in its entirety. Organic-inorganic titanate hybrid pigments are available as Tico™ pigments from Heubach GmbH. However, certain Tico™ pigments are not suitable for use in high temperature applications, such as in nylon molding compositions.